Multi-layer polyolefin shrink film

ABSTRACT

A five layered thermoplastic film may be utilized to form storm windows or packaging material. A preferred embodiment of the film comprises a core layer consisting essentially of either (a) a copolymer of ethylene and vinyl acetate or (b) a three component blend of (a) a linear low density polyethylene, (b) a linear medium density polyethylene and (c) an ethylene vinyl acetate copolymer. The preferred embodiment also comprises two intermediate layers each consisting essentially of a linear low density polyethylene, and two surface layers each consisting essentially of either a four component blend of (1) a linear low density polyethylene, (2) a linear medium density polyethylene, (3) a copolymer of ethylene and vinyl acetate and (4) one or more light stabilizers, or a three component blend in which light stabilizers are not present.

This application is a continuation-in-part of U.S. Ser. No. 615,418,filed May 30, 1984, now U.S. Pat. No. 4,514,465.

FIELD OF THE INVENTION

The present invention relates to an elastic and heat shrinkablethermoplastic film which may be utilized as a storm window. The film mayalso be utilized as a packaging material. A preferred embodiment of thepresent invention comprises a palindromic five layer film having a corelayer comprising either (a) an ethylene vinyl acetate copolymer or (b) athree component blend of (1) a linear low density polyethylene, (2) alinear medium density polyethylene and (3) an ethylene vinyl acetatecopolymer. The core layer is located between two intermediate layerseach of which comprise a linear low density polyethylene. Two surfacelayers each comprising a four component blend of (1) a linear lowdensity polyethylene, (2) a linear medium density polyethylene, (3) anethylene vinyl acetate copolymer and (4) one or more ultraviolet lightstabilizers are also present in the preferred embodiment. A desiredcombination of physical characteristics beneficially results from thisstructure.

BACKGROUND OF THE INVENTION

The present invention is directed to new and useful multi-layer heatshrinkable film formulations. One distinguishing feature of a heatshrink film is the film's ability, upon exposure to a certaintemperature, to shrink or, if restrained from shrinking, to generateshrink tension within the film.

The manufacture of shrink films, as is well known in the art, may begenerally accomplished by the extrusion (single and multi-layer films)or coextrusion (multi-layer films) of thermoplastic resinous materialswhich have been heated to their flow or melting point from an extrusionor coextrusion die in, for example, either tubular or planer (sheet)form. After a post extrusion quenching to cool by, for example, thewell-known cascading water method, the relatively thick "tape" extrudateis then reheated to a temperature within its orientation temperaturerange and stretched to orient or align the crystallites and/or moleculesof the material. The orientation temperature range for a given materialor materials will vary with the different resinous polymers and/orblends thereof which comprise the material. However, the orientationtemperature range for a given thermoplastic material may generally bestated to be below the crystalline melting point of the material butabove the second order transition temperature (sometimes referred to asthe glass transition point) thereof. Within this temperature range anorientable material may be effectively oriented.

The terms "orientation" or "oriented" are used herein to generallydescribe the process step and resultant product characteristics obtainedby stretching and immediately cooling a resinous thermoplastic polymericmaterial which has been heated to a temperature within its orientationtemperature range so as to revise the molecular configuration of thematerial by physical alignment of the crystallites and/or molecules ofthe material to improve certain mechanical properties of the film suchas, for example, shrink tension and orientation release stress. Both ofthese properties may be measured in accordance with ASTM D 2838-81. Whenthe stretching force is applied in one direction uniaxial orientationresults. When the stretching force is applied in two directions biaxialorientation results. The term oriented is also used hereininterchangeably with the term "heat shrinkable" with these termsdesignating a material which has been stretched and set by cooling whilesubstantially retaining its stretched dimensions. An oriented (i.e. heatshrinkable) material will tend to return to its original unstretched(unextended) dimensions when heated to an appropriate elevatedtemperature.

Returning to the basic process for manufacturing the film as discussedabove, it can be seen that the film, once extruded (or coextruded if itis a multi-layer film) and initially cooled to by, for example,cascading water quenching, is then reheated to within its orientationtemperature range and oriented by stretching. The stretching to orientmay be accomplished in many ways such as, for example, by "blown bubble"techniques or "tenter framing". These processes are well known to thosein the art and refer to orientation procedures whereby the material isstretched in the cross or transverse direction (TD) and/or in thelongitudinal or machine direction (MD). After being stretched, the filmis quickly quenched while substantially retaining its stretcheddimensions to rapidly cool the film and thus set or lock-in the oriented(aligned) molecular configuration.

Of course, if a film having little or no orientation is desired, e.g.non-oriented or non-heat shrinkable film, the film may be formed from anon-orientable material or, if formed from an orientable material may be"hot blown". In forming a hot blown film the film is not cooledimmediately after extrusion or coextrusion but rather is first stretchedshortly after extrusion while the film is still at an elevatedtemperature above the orientation temperature range of the material.Thereafter, the film is cooled, by well-known methods. Those of skill inthe art are well familiar with this process and the fact that theresulting film has substantially unoriented characteristics. Othermethods for forming unoriented films are well known. Exemplary, is themethod of cast extrusion or cast coextrusion which, likewise, is wellknown to those in the art.

If an orientable material is utilized, the degree of stretching controlsthe degree or amount of orientation present in a given film. Greaterdegrees of orientation are generally evidenced by, for example,increased values of shrink tension and orientation release stress. Thatis, generally speaking, for films manufactured from the same materialunder otherwise similar conditions, those films which have beenstretched, e.g. oriented, to a greater extent will exhibit larger valuesfor free shrink, shrink tension and/or orientation release stress. Asstated above, the last two values are to be measured in accordance withASTM-D-2838-81. The first value should be measured in accordance withASTM D 2732-70 (reapproved 1976).

After setting the stretch-oriented molecular configuration the film maythen be stored in rolls and utilized to tightly package a wide varietyof items. In this regard, the product to be packaged may first beenclosed in the heat shrinkable material by heat sealing the shrink filmto itself where necessary and appropriate to form a pouch or bag andthen inserting the product therein and closing the bag or pouch by heatsealing or other appropriate means such as, for example, clipping. Ifthe material was manufactured by "blown bubble" techniques the materialmay still be in tubular form or it may have been slit and opened up toform a sheet of film material. Alternatively, a sheet of the materialmay be utilized to over-wrap the product which may be in a tray. Thesepackaging methods are all well known to those of skill in the art.Thereafter, the enclosed product may be subjected to elevatedtemperatures by, for example, passing the enclosed product through a hotair or hot water tunnel. This causes the enclosing film to shrink aroundthe product to produce a tight wrapping that closely conforms to thecontour of the product. As stated above, the film sheet or tube may beformed into bags or pouches and thereafter utilized to package aproduct. In this case, if the film has been formed as a tube it may bepreferable to first slit the tubular film to form a film sheet andthereafter form the sheet into bags or pouches. Such bag or pouchforming methods, likewise, are well known to those of skill in the art.

Another alternative use for heat shrink film is in the formation of lowcost storm windows. In this application a sheet of the material may beattached to the window frame and thereafter heat shrunk, for example byusing a hand held electric hair dryer, to tighten the film and improvethe overall appearance of the window. Alternatively, the film may bestretched across the window casement or housing and attached theretowithout post attachment heat shrinking.

The above general outline for manufacturing of films is not meant to beall inclusive since such processes are well known to those in the art.For example, see U.S. Pat. Nos. 4,274,900; 4,229,241; 4,194,039;4,188,443; 4,048,428; 3,821,182 and 3,022,543. The disclosures of thesepatents are generally representative of such processes and are herebyincorporated by reference.

Alternative methods of producing films of this type are known to thosein the art. One well-known alternative is the method of forming amulti-layer film by an extrusion coating rather than by an extrusion orcoextrusion process as was discussed above. In extrusion coating a firsttubular layer is extruded and thereafter an additional layer or layersis sequentially coated onto the outer surface of the first tubular layeror a successive layer. Exemplary of this method is U.S. Pat. No.3,741,253. This patent is generally representative of an extrusioncoating process and is hereby incorporated by reference.

Many other process variations for forming films are well known to thosein the art. For example, multiple layers may be first coextruded withadditional layers thereafter being extrusion coated thereon. Or twomulti-layer tubes may be coextruded with one of the tubes thereafterbeing extrusion coated or laminated onto the other. The extrusioncoating method of film formation may be preferable to coextruding theentire film when it is desired to subject one or more layers of the filmto a treatment which may be harmful to one or more of the other layers.Exemplary of such a situation is a case where it is desired to irradiateone or more layers of a film containing an oxygen barrier layercomprised of one or more copolymers of vinylidene chloride and vinylchloride. Those of skill in the art generally recognize that irradiationis generally harmful to such oxygen barrier layer compositions.Accordingly, by means of extrusion coating, one may first extrude orcoextrude a first layer or layers, subject that layer or layers toirradiation and thereafter extrusion coat the oxygen barrier layer and,for that matter, other layers sequentially onto the outer surface of theextruded previously irradiated tube. This sequence allows for theirradiation cross-linking of the first layer or layers withoutsubjecting the oxygen barrier layer or other sequentially added layersto the harmful effects thereof.

Irradiation of an entire film or a layer or layers thereof may bedesired so as to improve the film's resistance to abuse and/or punctureand other physical characteristics. It is generally well known in theart that irradiation of certain film materials results in thecross-linking of the polymeric molecular chains contained therein andthat such action generally results in a material having improved abuseresistance. When irradiation is employed to accomplish thecross-linking, it may be accomplished by the use of high energyirradiation using electrons, X-rays, gamma rays, beta rays, etc.Preferably, electrons are employed of at least about 10⁴ electron voltenergy. The irradiation source can be a Van der Graaff electronaccelerator, e.g. one operated, for example, at about 2,000,000 voltswith a power output of about 500 watts. Alternatively, there can beemployed other sources of high energy electrons such as the GeneralElectric 2,000,000 volt resonant transformer or the corresponding1,000,000 volt, 4 kilowatt, resonant transformer. The voltage can beadjusted to appropriate levels which may be, for example, 1,000,000 or2,000,000 or 3,000,000 or 6,000,000 or higher or lower. Other apparatusfor irradiating films are known to those of skill in the art. Theirradiation is usually carried out at between about one megarad andabout 75 megarads, with a preferred range of about 8 megarads to about20 megarads. Irradiation can be carried out conveniently at roomtemperature, although higher and lower temperatures, for example, about0° C. to about 60° C. may be employed.

Cross-linking may also be accomplished chemically through utilization ofperoxides as is well known to those of skill in the art. A generaldiscussion of cross-linking can be found at pages 331 to 414 of volume 4of the Encyclopedia of Polymer Science and Technology, Plastics, Resins,Rubbers, Fibers published by John Wiley & Sons, Inc. and copyrighted in1966. This document has a Library of Congress Catalog Card No. of64-22188.

Another possible processing variation is the application of a fine mistof a silicone or anti-fog spray to the interior of the freshly extrudedtubular material to improve the further processability of the tubularmaterial. A method and apparatus for accomplishing such internalapplication is disclosed in a European patent application underpublication No. of 0071349A2. This document was published on or aboutFeb. 9, 1983 and discloses the application of a coating of apolyorganosiloxane onto the internal surface of monolayer tubular linearpolyethylene films.

The polyolefin family of shrink films and, in particular, thepolyethylene family of shrink films provide a wide range of physical andperformance characteristics such as, for example, shrink force (theamount of force that a film exerts per unit area of its cross-sectionduring shrinkage), the degree of free shrink (the reduction in lineardimension in a specified direction that a material undergoes whensubjected to elevated temperatures while unrestrained), tensil strength(the highest force that can be applied to a unit area of film before itbegins to tear apart), heat sealability (the ability of the film to heatseal to itself or another given surface), shrink temperature curve (therelationship of shrink to temperature), tear initiation and tearresistance (the force at which a film will begin to tear and continue totear), optics (gloss, haze and transparency of material), elongation(the degree the film will stretch or elongate at room temperature),elastic memory (the degree a film will return to its originalunstretched (unelongated) dimension after having been elongated at roomtemperature), and dimensional stability (the ability of the film toretain its original dimensions under different types of storageconditions). Film characteristics play an important role in theselection of a particular film and they may differ from each filmapplication.

In view of the many above-discussed physical characteristics which areassociated with polyolefin films and films containing a polyolefinconstituent and in further view of the numerous applications with whichthese films have already been associated and those to which they may beapplied in the future, it is readily discernable that the need for everimproving any or all of the above described physical characteristics orcombinations thereof in these films is great, and, naturally, ongoing.In particular, the quest for films which may be utilized as a low coststorm window material has been ongoing since such a film applicationcould compete well with the much more expensive permanent glass stormwindows which have been historically utilized. A low cost heat shrinkstorm window film should preferably possess (1) good opticalcharacteristics so that the function of the window is not undesirablydegraded, (2) high physical abuse resistance, (3) good resistance todegradation from light, (4) good elongation (so that it may be stretchedtightly onto the window frame prior to attachment thereto), (5) goodelastic memory (so that it will not readily permanently deform whensubjected to the forces of nature--e.g. wind, rain, small debris) and(6) a low to moderate degree of orientation (so that, if desired, thefilm may be shrunk into tight configuration with the window framewithout generating an undesirable degree of tension within the film).Orientation also provides the film with improved physicalcharacteristics such as, for example, good tensile strength.

In particular, the present multilayer film is preferable to a presentlymanufactured monolayer storm window film which should be utilized onlyon the interior side of the window. This prior art monolayer filmpreferably comprises a single layer of linear medium densitypolyethylene material having a polyorganosiloxane coating on one sidethereof. For details of this film reference should be made to theabove-identified European Patent Application Publication No. 0071349A2.

Other prior art films utilizing linear polyethylene materials and blendsthereof are known to those of skill in the art. Exemplary multilayerprior art films having a core layer of linear low density polyethylenematerial are U.S. Pat. No. 4,364,981 to Horner which discusses a threelayer film having a core layer of low pressure, low density polyethylene(LLDPE) and outer layers of high pressure, low density polyethylene(conventional low density polethylene) and U.S. Pat. No. 4,399,180 toBriggs which discusses a stretch-wrap film having a core layer of linearlow density polyethylene with a layer, on at least one side, comprisinga highly branched low density polyethylene. U.S. Pat. No. 4,399,173 toAnthony discusses a multilayer film comprising a core layer of low meltindex, low pressure, low density polyethylene and two outer layers of ahigh melt index, low pressure, low density polyethylene. U.S. Pat. No.4,425,268 to Cooper discloses a composition adapted for processing intostretch-wrap film. Generally, the Cooper composition comprises a blendof an ethylene vinyl acetate copolymer and a linear low densitypolyethylene material. The material may also contain a tackifier.

OBJECTS OF THE PRESENT INVENTION

Accordingly, it is a general object of the present invention to providean elastic heat shrinkable film which is useful as a low cost stormwindow. The film may also be utilized in conventional packagingapplications, if desired.

It is another object of the present invention to provide an elastic heatshrinkable film having a desired new and improved combination ofphysical characteristics such as, for example, a low degree oforientation or heat shrinkability combined with good puncture and tearresistance along with good elongation and elastic memory (elasticity orsnap-back).

Yet another object of the present invention is to provide an elasticfive layer heat shrink film having a core layer comprising either (a) anethylene vinyl acetate copolymer or (b) a three component blend of (1) alinear low density polyethylene, (2) a linear medium densitypolyethylene and (3) an ethylene vinyl acetate copolymer; twointermediate layers each comprising a linear low density polyethylene,with the core layer being located between the two intermediate layersand two surface layers each comprising a four component blend of (1) alinear low density polyethylene, (2) a linear medium densitypolyethylene, (3) an ethylene vinyl acetate copolymer and (4) one ormore ultraviolet stabilizers.

Still another object of the present invention is to provide an elasticfive layer palindromic film having a core layer consisting essentiallyof either (1) an ethylene vinyl acetate copolymer or (b) a threecomponent blend of (1) linear low density polyethylene, (2) linearmedium density polyethylene and (3) an ethylene vinyl acetate copolymer;two intermediate layers each consisting essentially of a linear lowdensity polyethylene and two surface layers each consisting essentiallyof a four component blend of (1) a linear low density polyethylene, (2)a linear medium density polyethylene, (3) an ethylene vinyl acetatecopolymer and (4) one or more ultraviolet stabilizers.

An even further object of the present invention is to provide an elasticfive layer heat shrink palindromic film comprising a core layercomprising either (a) an ethylene vinyl acetate copolymer or (b) a threecomponent blend of (1) from about 40% to about 60%, by weight, of linearlow density polyethylene, (2) from about 20% to about 30%, by weight, oflinear medium density polyethylene and (3) from about 20% to about 30%,by weight, of an ethylene vinyl acetate copolymer; two intermediatelayers each comprising linear low density polyethylene and two surfacelayers each comprising a four component blend of (1) from about 40% toabout 60%, by weight, of linear low density polyethylene, (2) from about20% to about 30%, by weight, of linear medium density polyethylene, (3)from about 20% to about 30%, by weight, of an ethylene vinyl acetatecopolymer and (4) from about 500 to about 3,000 ppm (parts per million)of one or more ultraviolet stabilizers.

One other object of the present invention is to provide an elastic fivelayer heat shrink palindromic film comprising a core layer consistingessentially of either (a) an ethylene vinyl acetate copolymer or (b) athree component blend of (1) from about 40% to about 60%, by weight, oflinear low density polyethylene, (2) about 20% to about 30%, by weight,linear medium density polyethylene and (3) from about 20% to about 30%,by weight, of an ethylene vinyl acetate copolymer; two intermediatelayers each consisting essentially of about 100%, by weight, of linearlow density polyethylene and two surface layers each consistingessentially of a four component blend of (1) from about 40% to about60%, by weight, of linear low density polyethylene, (2) from about 20%to about 30%, by weight, of linear medium density polyethylene, (3) fromabout 20% to about 30%, by weight, of an ethylene vinyl acetatecopolymer and (4) from about 500 to about 3,000 ppm of one or moreultraviolet stabilizers.

Yet a further object of the present invention is to provide an elasticfive layer heat shrink palindromic film adapted for use as a stormwindow which comprises a core layer consisting essentially of either (a)about 100%, by weight, of an ethylene vinyl acetate copolymer or (b) athree component blend of (1) about 55%, by weight, of a linear lowdensity polyethylene, (2) about 28%, by weight, of a linear mediumdensity polyethylene and (3) about 17%, by weight, of an ethylene vinylacetate copolymer; two intermediate layers each consisting essentiallyof about 100%, by weight, of a linear low density polyethylene and twosurface layers each consisting essentially of a four component blend of(1) about 50%, by weight, linear low density polyethylene, (2) about25%, by weight, of linear medium density polyethylene, (3) about 25%, byweight, of an ethylene vinyl acetate copolymer and (4) about 1,500 ppmof a hindered amine ultraviolet light stabilizer.

An additional object of the present invention is to provide an elasticfive layer heat shrinkable film having a desired new and improvedcombination of physical characteristics such as, for example arelatively high degree of orientation or heat shrinkability.

One other object of the present invention is to provide an elastic fivelayer heat shrinkable film having a core layer comprising either (a) anethylene vinyl acetate copolymer or (b) a three component blend of (1) alinear low density polyethylene (2) a linear medium density polyethyleneand (3) an ethylene vinyl acetate copolymer; two intermediate layerseach comprising a linear low density polyethylene, with the core layerbeing located between the two intermediate layers; and two surfacelayers each comprising a three component blend of (1) a linear lowdensity polyethylene, (2) a linear medium density polyethylene, and (3)an ethylene vinyl acetate copolymer.

It is yet a further object of the present invention to provide a heatshrinkable film as described immediately above wherein the film isstretch oriented or biaxially oriented in the range of from about 4.0 toabout 6.0 times the original dimensions in both the transverse (TD) andlongitudinal (MD) directions.

Still further objects and the broad scope of applicability of thepresent invention will become apparent to those of ordinary skill in theart from the details disclosed hereinafter. However, it should beunderstood that the following detailed description which indicates thepresently preferred embodiment of the present invention is only givenfor purposes of illustration since various changes and modificationswell within the scope of the present invention will become apparent tothose of ordinary skill in the art in view of the following detaileddescription.

DEFINITIONS

Unless specifically set forth and defined or otherwise limited, theterms "polymer" or "polymer resin" as used herein generally include, butare not limited to, homopolymers, copolymers, such as, for exampleblock, graft, random and alternating copolymers, terpolymers etc. andblends and modifications thereof. Furthermore, unless otherwisespecifically limited the terms "polymer" or "polymer resin" shallinclude all possible symmetrical structures of the material. Thesestructures include, but are not limited to, isotactic, syndiotactic andrandom symmetries.

The term "melt flow" as used herein is the amount, in grams, of athermoplastic resin which can be forced through a given orifice under aspecified pressure and temperature within ten minutes. The value shouldbe determined in accordance with ASTM D 1238-79. The term "melt flowindex" refers specifically to the value obtained in accordance withcondition E of ASTM D 1238-79.

The terms "surface" or "surface layer" or "skin" or "skin layer" as usedherein means a layer of a multi-layer film which comprises a surfacethereof.

The term "interior" or "interior layer" as used herein refers to a layerof a multi-layer film which is not a skin or surface layer of the film.

The term "core" or "core layer" as used herein refers to an interiorlayer of a multi-layer film having an odd number of layers wherein thesame number of layers is present on either side of the core layer.

The term "intermediate" or "intermediate layer" as used herein refers toan interior layer of a multi-layer film which is positioned between acore layer and a surface layer of said film.

The term "palindromic" film as used herein refers to a multi-layer filmthe layer configuration of which is substantially symmetrical. Examplesof palindromic films would be films having the following layerconfigurations: (1) A/B/A, (2) A/B/B/A, (3) A/B/C/B/A, etc. An exampleof a non-palindromic film layer configuration would be a film having alayer configuration of A/B/C/A.

The term polyolefin as used herein refers to polymers of relativelysimple olefins such as, for example, ethylene, propylene, butenes,isoprenes and pentenes; including, but not limited to, homopolymers,copolymers, blends and modifications of such relatively simple olefins.

The term "polyethylene" as used herein refers to a family of resinsobtained by polymerizing the gas ethylene, C₂ H₄. By varying thecatalysts and methods of polymerization, properties such as density,melt index, crystallinity, degree of branching and cross-linking,molecular weight and molecular weight distribution can be regulated overwide ranges. Further modifications are obtained by copolymerization,chlorination, and compounding additives. Low molecular weight polymersof ethylene are fluids used as lubricants; medium weight polymers arewaxes miscible with paraffin; and the high molecular weight polymers(generally over 6,000) are resins generally used in the plasticsindustry. Polyethylenes having densities ranging from about 0.900 gramsor less per cubic centimeter to about 0.925 grams per cubic centimeterare called low density polyethylenes with those having densities fromabout 0.926 grams per cubic centimeter to about 0.940 grams per cubiccentimeter being called medium density polyethylenes. Polyethyleneshaving densities of from about 0.941 grams per cubic centimeter to about0.965 grams per cubic centimeter and over are generally called highdensity polyethylenes. Conventional low density types of polyethylenesare usually polymerized at high pressures and temperatures whereasconventional high density polyethylenes are usually polymerized atrelatively low temperatures and pressures. The molecular structure ofconventional low density polyethylenes is highly branched. Whileconventional medium density polyethylenes possess a molecular structurewhich is branched, the degree of branching is less than that ofconventional low density polyethylenes. The molecular structure of highdensity polyethylenes generally possess little or no side branching.

The terms "linear low density polyethylene" or "linear medium densitypolyethylene" as used herein refer to copolymers of ethylene with one ormore comonomers selected from C₄ to C₁₀ alpha olefins such as butene-1,octene, etc. in which the molecules of the copolymers comprise longchains with few side chains, branches or cross-linked structures. Thismolecular structure is to be contrasted with conventional low or mediumdensity polyethylenes which are more highly branched than theirrespective linear counterparts. Moreover, the side branching which ispresent in linear low or linear medium density polyethylenes will beshort as compared to the respective conventional polyethylenes. Themolecular chains of a linear polymer may be intertwined, but the forcestending to hold the molecules together are believed to be physicalrather than chemical and thus may be weakened by energy applied in theform of heat. Linear low density polyethylene as defined herein has adensity usually in the range of from about 0.900 or less grams per cubiccentimeter to about 0.925 grams per cubic centimeter and, preferably,the density should be maintained between 0.916 grams per cubiccentimeter to 0.925 grams per cubic centimeter. Linear medium densitypolyethylene, as defined herein, has a density usually in the range offrom about 0.926 grams per cubic centimeter to about 0.941 grams percubic centimeter. The melt flow index of linear low and medium densitypolyethylenes generally ranges from between about 0.1 to about 10 gramsper ten minutes and preferably between from about 0.5 to about 3.0 gramsper ten minutes. Linear low and linear medium density polyethyleneresins of this type are commercially available and are manufactured inlow pressure vapor phase and liquid phase processes using transitionmetal catalysts.

The term "ethylene vinyl acetate copolymer" (EVA) as used herein refersto a copolymer formed from ethylene and vinyl acetate monomers whereinthe ethylene derived units in the copolymer are present in major amountsand the vinyl acetate derived units in the copolymer are present inminor amounts.

An "oriented" or "heat shrinkable" material is defined herein as amaterial which, when heated to an appropriate temperature above roomtemperature (for example 96° C.), will have a free shrink of 5% orgreater in at least one linear direction.

All compositional percentages used herein are calculated on a "byweight" basis.

Density should be measured in accordance with ASTM D 1505-68 (reapproved1979).

Free shrink should be measured in accordance with ASTM D 2732.

Shrink tension and orientation release stress should be measured inaccordance with ASTM D 2838-81.

The tensile properties of the film should be measured in accordance withASTM D 882-81.

The elongation properties of the film should be measured in accordancewith ASTM D 638.

The haze and luminous transmittance of the film should be measured inaccordance with ASTM D 1003-61 (reapproved 1971).

The specular gloss of the film should be measured in accordance withASTM D 2457-70 (reapproved 1977).

The tear propagation of the film should be measured in accordance withASTM D 1938-67 (reapproved 1978).

The impact resistance of the film should be measured in accordance withASTM D 3420-80.

One method for determining whether a material is "cross-linked" is toreflux the material in boiling toluene or xylene, as appropriate, forforty (40) hours. If a weight percent residue of at least 5 percentremains the material is deemed to be cross-linked. A procedure fordetermining whether a material is cross-linked vel non is to reflux 0.4gram of the material in boiling toluene or another appropriate solvent,for example xylene, for twenty (20) hours. If no insoluble residue (gel)remains the material may not be cross-linked. However, this should beconfirmed by the "melt flow" procedure below. If, after twenty (20)hours of refluxing insoluble residue (gel) remains the material isrefluxed under the same conditions for another twenty (20) hours. Ifmore than 5 weight percent of the material remains upon conclusion ofthe second refluxing the material is considered to be cross-linked.Preferably, a least two replicates are utilized. Another method wherebycross-linking vel non and the degree of cross-linking can be determinedis by ASTM-D-2765-68 (Reapproved 1978). Yet another method fordetermining whether a material is cross-linked vel non is to determinethe melt flow of the material in accordance with ASTM D 1238-79 at 230°Centigrade while utilizing a 21,600 gram load. Materials having a meltflow of greater than 75 grams per ten minutes shall be deemed to thenon-cross-linked. This method should be utilized to confirm the "gel"method described above whenever the remaining insoluble gel content isless than 5% since some cross-linked materials will evidence a residualgel content of less than 5 weight percent. If the cross-linking isaccomplished by irradiation of the film the amount of ionizing radiationwhich has been absorbed by a known film material can be calculated bycomparing the weight percent of insoluble material (gel) remaining afterrefluxing the sample to the weight percents of gel remaining afterrefluxing standards of the same material which have been irradiated todifferent known degrees. Those of skill in the art also recognize that acorrelation exists between the amount of ionizing irradiation absorbedand the melt flow of a material. Accordingly, the amount of ionizingirradiation which a material has absorbed may be determined by comparingthe melt flow of the material to the melt flow of samples of the samematerial which have been irradiated to different known degrees.

The term "crystalline" or "crystalline polymer" material, etc. as usedherein refers to a polymeric material which is composed of molecularchains which are so constructed that they can pack together well inordered arrangements. The finite volume throughout which the orderextends is designated by the term "crystallite" with the surroundingdisordered regions, if any, being designated by the term "amorphous".The crystallites are denser than the surrounding amorphous regions ofthe material and also have a higher refractive index. If a crystallinematerial is oriented the crystallites become generally aligned with eachother. Three well known methods for determining the degree ofcrystallinity are by (1) (a) measuring the specific volume of thespecimen (V), (b) measuring the specific volume of the crystallites (Vc)within the specimen and (c) measuring the specific volume of theamorphous region (Va) contained within the specimen and then utilizingthe equation [% crystallinity=(Va-V)/(Va-Vc)], (2) X-ray diffractionmethods and (3) infrared absorption methods. All of these methods arewell known to those in the art. A general discussion of crystallinitycan be found at pages 449 to 527 of volume 4 of the Encyclopedia ofPolymer Science and Technology, Plastics, Resins, Rubbers, Fiberspublished by John Wiley & Sons, Inc. and copyrighted in 1966. Thisdocument has a Library of Congress Catalogue Card No. of 64-22188.

The term "gauge" is a unit of measure applied to the thickness of filmsor the layers thereof. 100 gauge is equal to 1 mil which is onethousandth of an inch.

A rad is the quantity of ionizing radiation that results in theabsorption of 100 ergs of energy per gram of a radiated material,regardless of the source of the radiation. A megarad is 10⁶ rads. (MR isan abbreviation for megarad.)

The term "yield point" as used herein refers to the percentage ofstretch a film may be subjected to without evidencing significantpermanent deformation. For example, a film with a yield point of 10%would substantially return to its original unstretched dimensions ifstretched 9%. The same film would not substantially return to itsoriginal unstretched dimensions if stretched 15%.

SUMMARY OF THE INVENTION

It has been discovered that a flexible, heat shrinkable thermoplasticfilm having a desirable combination of physical characteristics such as,a low degree of orientation or heat shrinkability, good elongation of atleast from about 100% to about 300% or greater, good puncture and tearresistance, good elastic memory, e.g. snap-back or elastic recovery(Preferably the film has a yield point in the range of from about 5%elongation to about 15% elongation.), and good resistance to lightdegradation has been achieved by the flexible film of the presentinvention. The film may be preferably utilized as a low cost stormwindow. The film may also be used in film packaging applications.

The film comprises a core layer comprising either (a) an ethylene vinylacetate copolymer or (b) a three component blend of (1) a linear lowdensity polyethylene, (2) a linear medium density polyethylene and (3)an ethylene vinyl acetate, copolymer; two intermediate layers eachcomprising a linear low density polyethylene and two surface layers eachcomprising a four component blend of (1) a linear low densitypolyethylene, (2) a linear medium density polyethylene, (3) an ethylenevinyl acetate copolymer and (4) one or more ultraviolet stabilizers. Apreferred embodiment of the film comprises a core layer consistingessentially of either (a) an ethylene vinyl acetate copolymer or (b) athree component blend of (1) from about 40% to about 60%, by weight, ofa linear low density polyethylene, (2) from about 20% to about 30%, byweight of a linear medium density polyethylene and (3) from about 20%,by weight, to about 30%, by weight, of an ethylene vinyl aetatecopolymer; two intermediate layers each consisting essentially of alinear low density polyethylene and two surface layers each consistingessentially of a four component blend of (1) from about 40% to about60%, by weight, of a linear low density polyethylene, (2) from 20% toabout 30%, by weight, linear medium density polyethylene, (3) from about20% to about 30%, by weight, of an ethylene vinyl acetate copolymer and(4) from about 500-3,000 parts per million of one or more ultravioletstabilizers. The most preferred embodiment of the present invention is afive layered film comprising a core layer which consists essentially ofeither (a) about 100%, by weight, of an ethylene vinyl acetate copolymerhaving from about 3.3% to about 4.1% vinyl acetate derived units and adensity of from about 0.9232 to about 0.9250 grams per cubic centimeteror (b) a three component blend of (1) about 55%, by weight, of a linearlow density polyethylene which is a copolymer of ethylene and octenehaving a density of about 0.920 grams per cubic centimeter, (2) about28%, by weight, of a linear medium density polyethylene having a densityof about 0.935 grams per cubic centimeter and (3) about 17%, by weight,of an ethylene vinyl acetate copolymer having from about 3.3% to about4.1% vinyl acetate derived units and a density of from about 0.9232 toabout 0.9250 grams per cubic centimeter; two intermediate layers eachcomprising about 100%, by weight, of linear low density polyethylenewhich is a copolymer of ethylene and octene having a density of about0.920 grams per cubic centimeter and two surface layers each consistingessentially of a four component blend of (1) about 50%, by weight, of alinear low density polyethylene which is a copolymer of ethylene andoctene having a density of about 0.920 grams per cubic centimeter, (2)about 25%, by weight, of a linear medium density polyethylene having adensity of about 0.935 grams per cubic centimeter, (3) about 25%, byweight, of a ethylene vinyl acetate copolymer having from about 3.3% toabout 4.1% vinyl acetate derived units and a density of from about0.9232-0.9250 grams per cubic centimeter and (4) about 1,500 parts permillion of a hindered amine ultraviolet light stabilizer.

Alternatively, a film especially useful in conventional packagingapplications comprises a core layer comprising either (a) an etheylenevinyl acetate copolymer or (b) a three component blend of (1) a linearlow density polyethylene, (2) a linear medium density polyethylene and(3) an ethylene vinyl acetate copolymer; two intermediate layers eachcomprising a linear low density polyethylene and two surface layers eachcomprising a three component blend of (1) a linear low densitypolyethylene, (2) a linear medium density polyethylene, and (3) anethylene vinyl acetate copolymer. A preferred embodiment of the filmcomprises a core layer consisting essentially of either (a) an ethylenevinyl acetate copolymer or (b) a three component blend of (1) from about40% to about 60%, by weight of a linear low density polyethylene, (2)from about 20% to about 30%, by weight of a linear medium densitypolyethylene and (3) from about 20%, by weight, to about 30%, by weight,of an ethylene vinyl acetate copolymer; two intermediate layers eachconsisting essentially of a linear low density polyethylene and twosurface layers each consisting essentially of a three component blend of(1) from about 40% to about 60%, by weight, of a linear low densitypolyethylene, (2) from about 20% to about 30%, by weight, linear mediumdensity polyethylene, and (3) from about 20% to about 30% by weight ofan ethylene vinyl acetate copolymer. The most preferred embodiment ofthe packaging film is a five layered film comprising a core layer whichconsists essentially of either (a) about 100%, by weight of an ethylenevinyl acetate copolymer having from about 3.3% to about 4.1% vinylacetate derived units and a density of from about 0.9232 to about 0.9250grams per cubic centimeter or (b) a three component blend of (1) about55%, by weight, of a linear low density polyethylene which is acopolymer of ethylene and octene having a density of about 0.920 gramsper cubic centimeter, (2) about 28%, by weight of a linear mediumdensity polyethylene having a density of about 0.935 grams per cubiccentimeter and (3) about 17%, by weight, of an ethylene vinyl acetatecopolymer having from about 3.3% to about 4.1% vinyl acetate derivedunits and a density of from about 0.9232 to about 0.9250 grams per cubiccentimeter; two intermediate layers each comprising about 100% by weightof linear low density polyethylene which is a copolymer of ethylene andoctene having a density of about 0.920 grams per cubic centimeter; andtwo surface layers each consisting essentially of a three componentblend of (1) about 50%, by weight, of a linear low density polyethylenewhich is a copolymer of ethylene and octene having a density of about0.920 grams per cubic centimeter, (2) about 25%, by weight, of a linearmedium density polyethylene having a density of about 0.935 grams percubic centimeter, and (3) about 25%, by weight, of an ethylene vinylacetate copolymer having from about 3.3% to about 4.1% vinyl acetatederived units and a density from about 0.9232 to 0.9250 grams per cubiccentimeter.

The film is both stretched, e.g. biaxially oriented, and cross-linked.Preferably the film is cross-linked by irradiation with from about 3.0to about 8.0 MR. A more preferable degree of cross-linking isaccomplished by irradiation of the film in the range of from about 5 toabout 7 MR. The most preferable degree of cross-linking is accomplishedby irradiation with about 6 MR.

In an alternate embodiment, in a film especially suited for conventionalpackaging applications, the film is cross-linked by irradiation withfrom about 1.0 to about 5.0 MR. A more preferable degree ofcross-linking is accomplished by irradiation of the packaging film inthe range of from about 2 to about 4 MR. The most preferable degree ofcross-linking is accomplished by irradiation with about 3 MR ofirradiation.

The degree of stretching to achieve the appropriate low degree ofbiaxial orientation and associated physical characteristics ispreferably in the range of from about 3.0 to about 4.0 times theoriginal dimensions in both the transverse (TD) and longitudinal (MD)directions. More preferably the degree of stretching is from about 3.0to about 3.5 times the original dimensions in both the transverse andlongitudinal directions. The most preferred degree of stretching, i.e.orientation, is approximately 3.3 times the original dimension in boththe transverse and longitudinal directions.

Alternatively, in a shrinkable film especially useful in conventionalpackaging applications, the degree of stretching to achieve theappropriate biaxial orientation and associated physical characteristicsis preferably in the range of from about 4.0 to about 6.0 times theoriginal dimensions in both the transverse (TD) and longitudinal (MD)directions. More preferably the degree of stretching is from about 4.5to about 5.5 times the original dimensions in both the transverse andlongitudinal directions. The most preferred degree of stretching, i.e.orientation, is approximately 5.0 times the original dimension in boththe transverse and longitudinal directions.

Preferably the thicknesses of the two skin layers are substantiallyequal to each other. The sum of the thicknesses of the two skin layersmay preferably range from about 20% to about 60% of the total thicknessof the film. More preferably the sum of the thicknesses of the two skinlayers may range from about 38% to about 48% of the total thickness ofthe film. Most preferably the sum of the thicknesses of the two skinlayers is about 43% of the total thickness of the film. That is, thethickness of each skin layer, most preferably, comprises about 21.5% ofthe total thickness of the film. Preferably the thicknesses of the twointermediate layers are substantially equal to each other. The sum ofthe thicknesses of the two intermediate layers may preferably range fromabout 20% to about 60% of the total thickness of the film. Morepreferably the sum of the thicknesses of the two intermediate layers mayrange from about 38% to about 48% of the total thickness of the film.Most preferably the sum of the thicknesses of the two intermediatelayers is about 43% of the total thickness of the film. That is, thethickness of each intermediate layer most preferably comprises about21.5% of the total thickness of the film. The thickness of the corelayer preferably ranges from about 10% to about 30% of the totalthickness of the film. More preferably the thickness of the core layermay range from about 12% to about 20% of the total thickness of thefilm. Most preferably the thickness of the core layer comprises about14% of the total thickness of the film.

Preferably, the total thickness of the film may range from about 50gauge to about 200 gauge. That is from about 0.50 mil to about 2.00 mil.More preferably the total thickness of the film may vary from about 50to about 100 gauge. Most preferably the film thickness is about 75gauge.

A colorant or dye may be added to any of the layers of the film.Preferably the colorant is only added to the intermediate and corelayers. More preferably the colorant is added only to the core layer.

The multi-layer film may be combined with other polymeric materials forspecific applications. For instance, additional layers may be added oneither or both sides of the film to improve various physicalcharacteristics.

BRIEF DESCRIPTION OF THE DRAWING

FIG. I is a cross-sectional view of a preferred five layered embodimentof the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. I, which is a cross-sectional view of a preferred fivelayered embodiment of the present invention, it is seen that thisembodiment comprises a core layer 1, two intermediate layers 2 and 3 andtwo skin or surface layers 4 and 5. The preferred thickness ratio of thefive layers of 21.5%/21.5%/14%/21.5%/21.5% is demonstrated in FIG. I.Preferred core layer 1 formulations comprise either (a) an ethylenevinyl acetate copolymer or (b) a three component blend of (1) a linearlow density polyethylene, (2) a linear medium density polyethylene and(3) and ethylene vinyl acetate copolymer. Preferably, core layer 1consists essentially of either (a) about 100%, by weight, of an ethylenevinyl acetate copolymer or (b) a three component blend of (1) from about40% to 60%, by weight, of a linear low density polyethylene, (2) fromabout 20% to about 30%, by weight, of a linear medium densitypolyethylene and (3) from about 20% to about 30%, by weight, of anethylene vinyl acetate copolymer. Most preferably the core layer 1consists essentially of either (a) about 100%, by weight, of an ethylenevinyl acetate copolymer having from about 3.3% to about 4.1% vinylacetate derived units and a density at 23° C. of from about 0.9232 toabout 0.9250 grams per cubic centimeter or (b) a three component blendof (1) about 55%, by weight, of a linear low density polyethylene whichis a copolymer of ethylene and octene and has a density at 23° C. ofabout 0.920 grams per cubic centimeter, (2) about 28%, by weight, of alinear medium density polyethylene having a density of 23° C. of about0.935 grams per cubic centimeter and (3) about 25%, by weight of anethylene vinyl acetate copolymer having from about 3.3% to about 4.1%vinyl acetate derived units and a density at 23° C. of from about 0.9232to about 0.9250.

As an especially preferred ethylene vinyl acetate copolymer which can beutilized in formulating the core layer 1 (as either the primaryconstituent thereof [one embodiment] or as a component in the threecomponent blend [second embodiment] both embodiments discussed above)may be obtained from the El Paso Polyolefins Company under the tradedesignation El Paso PE 204CS95. This material has a density at 23° C. offrom about 0.9232 to about 0.9250 grams per cubic centimeter and a meltflow (measured by ASTM D 1238, condition E-28) of about 2.0±0.5 gramsper ten (10) minutes. This material contains from about 3.3 to about4.1% vinyl acetate derived units. The nominal percent of vinyl acetatederived units present in the material is about 3.6%. Other ethylenevinyl acetate copolymers or blends of two or more ethylene vinyl acetatecopolymers may be utilized in either embodiment of the core layer 1 ofthe present invention. In particular, ethylene vinyl acetate copolymerscomprising from about 2%, by weight, to about 18%, by weight, vinylacetate derived units may be utilized. Preferably the ethylene vinylacetate copolymer will comprise from about 2%, by weight, to about 10%,by weight, of vinyl acetate derived units. Even more preferably theethylene vinyl acetate copolymer will comprise from about 2%, by weight,to about 5%, by weight, of vinyl acetate derived units.

With regard to the three component blend embodiment of core layer 1, anespecially preferred linear low density polyethylene may be obtainedfrom the Dow Chemical Company under the trade designation Dowlex 2045.This material is a copolymer of ethylene and octene and has a density at23° C. of about 0.920 grams per cubic centimeter and a melt flow index(measured by ASTM-D-1238, E-28) of from about 0.7 to about 1.2 grams perten minutes. Other linear low density polyethylene materials or blendsof two or more linear low density polyethylene materials may be utilizedas the linear low density polyethylene constituent of the three blendcomponent embodiment of core layer 1.

Preferably, the linear medium density polyethylene utilized in the threecomponent blend embodiment of core layer 1 has a density at 23° C. offrom about 0.933 to about 0.937 grams per cubic centimeter. Morepreferably the linear medium density polyethylene material has a densityat 23° C. of about 0.935 grams per cubic centimeter. A preferred linearmedium density polyethylene material for utilization in the core layerblend formulation may be obtained from the Dow Chemical Company underthe trade designation Dowlex 2037. This material is a copolymer ofethylene and octene and has a density at 23° C. of about 0.935 grams percubic centimeter and a flow rate (measured by ASTM-D-1238, conditionE-28) of 2.55±0.35 grams per ten (10) minutes. Other linear mediumdensity polyethylene materials or blends of two or more linear mediumdensity polyethylene materials may be utilized as the linear mediumdensity polyethylene constituent of the three component blend embodimentof core layer 1.

Intermediate layers 2 and 3 each comprise one or more linear low densitypolyethylenes. A preferred linear low density polyethylene materialwhich may be utilized in both of intermediate layers 2 and 3 may beobtained from the Dow Chemical Company under the trade designationDowlex 2045. This material is a copolymer of ethylene and octene and hasa density at 23° C. of about 0.920 grams per cubic centimeter and a meltflow index (ASTM-D-1238, E-28) of from about 0.7 to about 1.2 grams perten (10) minutes. Other linear low density polyethylenes or blends oftwo or more linear low density polyethylene materials may be utilized toformulate intermediate layers 2 and 3.

Returning to FIG. I, and in particular, to surface layers 4 and 5experimentation has determined that a preferred surface layerformulation should comprise a four component blend of (1) a linear lowdensity polyethylene material, (2) a linear medium density polyethylenematerial, (3) an ethylene vinyl acetate copolymer and (4) one or moreultraviolet light stabilizers. Alternatively, a heat shrinkable filmespecially useful in conventional packaging applications should includesurface layers 4 and 5 comprising a three component blend of (1) alinear low density polyethylene material, (2) a linear medium densitypolyethylene material, and (3) an ethylene vinyl acetate copolymer.

Preferably the formulation of each of the two skin layers 4 and 5comprises a four component blend of (1) from about 40% to about 60%, byweight, of a linear low density polethylene material (2) from about 20%to about 30%, by weight, of a linear medium density polyethylenematerial, (3) from about 20% to about 30%, by weight, of an ethylenevinyl acette copolymer and (4) one or more ultraviolet lightstabilizers.Even more preferably the surface layers of the film shouldcomprise a four component blend of (1) from about 45% to about 55%, byweight, of a linear low density polyethylene material, (2) from about23% to about 27%, by weight, of a linear medium density polyethylenematerial, (3) from about 23% to about 27%, by weight, of an ethylenevinyl acetate copolymer and (4) one or more ultraviolet stabilizers. Themost preferred skin or surface layer formulation of the presentinvention consists essentially of a four component blend of (1) about50%, by weight, of a linear low density polyethylene material, (2) about25%, by weight, of a linear medium density polyethylene material, (3)about 25%, by weight, of an ethylene vinyl acetate copolymer and (4) oneor more hindered amine ultraviolet stabilizers.

The same linear low density polyethylene resins which were discussedwith regard to the three component blend embodiment of core layer 1 andintermediate layers 2 and 3 may be utilized as the linear low densitypolyethylene constituent of the skin layers 4 and 5. However, the linearlow density polyethylene material used in the skin layers does not haveto be the material used in the core layer or intermediate layers.Accordingly, the film may comprise a first linear low densitypolyethylene material as a core layer constituent a second, different,linear low density polyethylene material as an intermediate layerconstituent and yet a third, different, linear low density polyethylenematerial as a constituent of the skin layers. Blends of one or morelinear low density polyethylene materials may comprise any linear lowdensity polyethylene constituent present in any layer. A preferredlinear low density polyethylene for utilization in the skin layers 4 and5 is Dowlex 2045, described in detail above. Preferably, the linearmedium density polyethylene of the skin layer has a density at 23° C. offrom about 0.933 to about 0.937 grams per cubic centimeter. Morepreferably the linear medium density polyethylene material has a densityat 23° C. of about 0.935 grams per cubic centimeter. A preferred linearmedium density polyethylene material for utilization in the surfacelayer formulation may be obtained from the Dow Chemical Company underthe trade designation Dowlex 2037. This material is a copolymer ofethylene and octene and has a density at 23° C. of about 0.935 grams percubic centimeter and a flow rate (measured by ASTM-D-1238, conditionE-28) of 2.55±0.35 grams per ten (10) minutes. Other linear low densitypolyethylene materials or blends of two or more linear low densitypolyethylene materials may be utilized as the linear low densitypolyethylene constituent of skin layers 4 and 5.

Ethylene vinyl acetae copolymers comprising from about 2%, by weight, toabout 18%, by weight, vinyl acetate derived units may be utilized as theethylene vinyl acetate component of skin layers 4 and 5. Preferably theethylene vinyl acetate copolymer will comprise from about 2%, by weight,to about 10%, by weight, of vinyl acetate derived units. Even morepreferably the ethylene vinyl acetate copolymer will comprise from about2%, by weight, to about 5%, by weight, of vinyl acetate derived units.The most preferred ethylene vinyl acetate copolymer for utilization inthe surface layer formulation may be obtained from the El PasoPolyolefins Company. This material has a density at 23° C. of from0.9232 to about 0.9250 grams per cubic centimeter and a melt flow(measure by ASTM D 1238, condition E-28) of about 2.0±0.5 grams per ten(10) minutes. The material contains from about 3.3 to about 4.1% vinylacetate derived units. The nominal percent of vinyl acetate derivedunits present in the material is about 3.6%. Blends of two or more ofthese ethylene vinyl acetate copolymers may be utilized as the ethylenevinyl acetate copolymer constituent of skin layers 4 and 5. Otherethylene vinyl acetate copolymers or blends thereof may also be utilizedas the ethylene vinyl acetate component of layers 4 and 5.

A preferred ultraviolet light stabilizer for utilization in skin layers4 and 5 may be obtained from Ciba-Geigy under the trade designationTINUVIN® 622. This material is a polymeric hindered amine, which isbelieved to have a molecular weight in excess of 2000 and a meltingrange of 130°-145° C. Published solubility data (grams per 100 grams ofsolution at 20° C.) for this material are: acetone 2, benzene 30,chloroform 40, ethyl acetate 5, hexane 0.01, methanol 0.1, methylenechloride 40, water 0.01, xylene 8. Preferably both surface layerscomprise from about 500 ppm (parts per million) to about 3,000 ppm ofthe ultraviolet light stabilizer. More preferably both layers comprisefrom about 1,000 to about 2,000 ppm of the light stabilizer. Mostpreferably both surface layers comprise about 1,500 ppm of the lightstabilizer. Blends of two or more hindered amine ultraviolet stabilizersmay be utilized as the ultraviolet light stabilizer constituent of skinlayers 4 and 5. Other ultraviolet light stabilizers or blends of one ormore other ultraviolet stabilizers may be utilized.

Preferably the composition and other parameters of intermediate layers 2and 3 are substantially the same. However, different linear low densitypolyethylenes may be utilized in each intermediate layer.

Preferably the composition and other parameters of skin layers 4 and 5are substantially the same. However, different linear low densitypolyethylene, linear medium density polyethylene, ethylene vinyl acetatecopolymers and ultraviolet stabilizers or blends thereof may be utilizedfor each skin layer.

Optionally a colorant or dye may be incorporated into all layers of thefilm. Preferably the dye is incorporated only into the core layer andintermediate layers. More preferably the dye is incorporated only intocore layer 1. Incorporating the dye into the interior layers of the filmreduces the possibility of the dye migrating to the surface of the film.The presence of the colorant reduces light transmission into the room orother area that is enclosed by the storm window. This features reducescooling requirements in warm climates. The option also may reduce glarefrom sunlight entering the room. Appropriate dyes/colorants are wellknown and available to those of skill in the art. In food packagingsituations FDA and/or USDA approved materials should be used.

Preferably the thicknesses of the two skin layers are substantiallyequal to each other. The sum of the thicknesses of the two skin layersmay preferably range from about 20% to about 60% of the total thicknessof the film. More preferably the sum of the thicknesses of the two skinlayers may range from about 38% to about 48% of the total thickness ofthe film. Most preferably the sum of the thicknesses of the two skinlayers is about 43% of the total thickness of the film. That is, thethickness of each skin layer, most preferably, comprises about 21.5% ofthe total thickness of the film. Preferably the thicknesses of the twointermediate layers are substantially equal to each other. The sum ofthe thicknesses of the two intermediate layers may preferably range fromabout 20% to about 60% of the total thickness of the film. Morepreferably the sum of the thicknesses of the two intermediate layers mayrange from about 38% to about 48% of the total thickness of the film.Most preferably the sum of the thicknesses of the two intermediatelayers is about 43% of the total thickness of the film. That is, thethickness of each intermediate layer most preferably comprises about21.5% of the total thickness of the film. The thickness of the corelayer preferably ranges from about 10% to about 30% of the totalthickness of the film. More preferably the thickness of the core layermay range from about 12% to about 20% of the total thickness of thefilm. Most preferably the thickness of the core layer comprises about14% of the total thickness of the film.

Preferably, the total thickness of the film may range from about 50gauge to about 200 gauge. That is from about 0.50 mil to about 2.00 mil.More preferably the total thickness of the film may vary from about 50to about 100 gauge. Most preferably the film thickness is about 75gauge.

Those skilled in the art will readily recognize that all of the byweight percentages disclosed herein are subject to slight variation.Additionally, these percentages may vary slightly as a result of theinclusion or application of additives to the surface layers such as thesilicone mist discussed above or inclusion therein of agents such asslip, antioxidant and anti-block agents. A preferred anti-block agent isa diatomaceous silica, SiO₂, which is available from McCullough &Benton, Inc. under the tradename Superfine Superfloss. This material hasa wet density of about 29.0 lbs/ft³, a specific gravity of about 2.30and a pH of about 9.5. Other well known antiblock agents may beutilized. A preferred slip agent is Erucamide (available from HumkoChemical under the tradename Kenamide E). This material is believed tohave an average molecular weight of about 335 and a melting point rangeof from about 72° C. to about 86° C. Other slip agents such asStearamide (available from the Humko Chemical Company under thetradename Kemamide S) and N,N-'-Dioleoylethylenediamine (available fromGlyco Chemical under the tradename Acrawax C) may be utilized. Apreferred silicone spray for application to the inner surface of theextruded tube is a liquid polyorganosiloxane manufactured by GeneralElectric under the trade designation General Electric SF18polydimethylsiloxane. A preferred antioxidant and thermal stabilizingagent is tetrakis[methylene3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane. This materialis believed to be a symmetrical molecule which includes four stericallyhindered phenolic hydroxyl groups and has a molecular weight of about1178. This material is available from by Ciba-Geigy under the tradedesignation Irganox® 1010.

The general ranges for inclusion of these agents into the surface layers4 and 5 and, in the case of the silicone spray, the application of thespray mist onto the interior surface layer of a tubular extrudate are asfollows:

(1) Anti-Block agent:

2000-4000 ppm, preferably

2500-3500 ppm, more preferably

about 3000 ppm, most preferably

(2) Slip Agent:

1000-2000 ppm, preferably

1250-1750 more preferably

about 1500 ppm most preferably

(b 3) Polydimethylsiloxane: 0.5 mg.ft² -and up

(4) Antioxidant:

100-500 ppm, preferably

200-400 ppm, more preferably

about 300 ppm, most preferably

When utilized within the specification and claims of the presentapplication the term "consisting essentially of" is not meant to excludeslight percentage variations or additives and agents of this sort.

Additional layers and/or minor amounts of various additives of the typesdescribed above may be added to the film structure of the presentinvention as desired but care must be taken not to adversely affect thedesired physical properties and other characteristics of the inventivefilm. It should also be recognized that many resins obtained from theirmanufacturer already contain small amounts of additives of differenttypes.

In the preferred process for making the multi-layer film of the presentinvention the basic steps are coextruding the layers to form amultilayer film, irradiating the film, and then stretching the film tobiaxially orient. These steps and additional desirable steps will beexplained in detail in the paragraphs which follow.

The process begins by blending, as necessary, the raw materials (i.e.polymeric resins) in the proportions and ranges desired as discussedabove. The resins are usually purchased from a supplier in pellet formand can be blended in any one of a number of commercially availableblenders as is well known in the art. During the blending process anyadditives and/or agents which are desired to be utilized are alsoincorporated. The additives may be incorporated into the blend byutilizing a masterbatch containing small percentages of the additives.For example, in the preferred embodiment of the present invention thelight stabilizer and antioxidant are added to the blend which will formthe surface layers by blending in a masterbatch available from Ampacetunder the trade designation 10478. This material comprises a threecomponent blend of (1) about 88%, by weight, conventional low densitypolyethylene having a density of about 0.918-0.922 grams per cubiccentimeter and a melt index of from about 6 to about 10 grams per tenminutes, (2) about 10%, by weight, of hindered amine light stabilizer(TINUVIN® 662) and (3) about 2%, by weight, of antioxidant (Irganox®1010).

The resins and applicable additives and/or agents are then fed to thehoppers of extruders which feed a coextrusion die. For the preferredpalindromic five layer film, wherein the two intermediate layers aresubstantially identical to each other and the two surface layers aresubstantially identical to each other, at least three extruders need tobe employed. One for the two substantially identical skin or surfacelayers, one for the two substantially identical intermediate layers andone for the core layer. Additional extruders may be employed if a filmhaving non-identical (e.g. non-palindromic film) intermediate and/orsurface layers is desired. The materials are coextruded as a relativelythick tube or "tape" which has an initial diameter and thicknessdependent upon the diameter and die gap of the coextrusion die. Thefinal diameter and thickness of the tubular film is dependent upon theracking ratio, e.g. the stretching ratio. Circular coextrusion dies arewell known to those in the art and can be purchased from a number ofmanufacturers. As an alternative to tubular coextrusion, slot dies couldbe used to coextrude the material in sheet form. Well known single ormulti-layer extrusion coating processes could also be utilized, ifdesired.

An additional process step which should be utilized to manufacture thepreferred embodiment of the presently inventive film is to irradiate thetape or unexpanded tubing or sheet by bombarding it with high-energyelectrons from an accelerator to cross-link the materials of the tube.Cross-linking increases the structural strength of the film and/or theforce at which the material can be stretched before tearing apart whenthe film materials are predominately ethylene such as conventionaland/or linear polyethylene (low, medium and high density) and/orcopolymers of ethylene such as, for example, ethylene vinyl acetate.Irradiation may also improve the optical properties of the film andchange the properties of the film at higher temperatures. A preferredirradiation dosage level is in the range of from about 3.0 MR to about8.0 MR. An even more preferred range is from about 5.0 MR to about 7.0MR. The most preferred dosage level is approximately 6.0 MR.

Following coextrusion, quenching to cool and solidify, and irradiationof the tape, the extruded tubular tape is reheated to its orientationtemperature range and inflated, by application of internal air pressure,into a bubble thereby transforming the narrow tubular tape with thickwalls into a wide tubular film with thin walls of the desired filmthickness and width. This process is sometimes referred to as the"trapped bubble technique" of orientation or as "racking". The degree ofinflation and subsequent stretching is often referred to as the "rackingratio" or "stretching ratio". For example, a transverse racking orstretching ratio of 2.0 would mean that the film had been stretched 2.0times its original extruded size in the transverse direction duringtransverse racking. After stretching, the tubular film is then collapsedinto a superimposed lay-flat configuration and wound into rolls oftenreferred to as "mill rolls". The racking process orients the film bystretching it transversely and, to some extent, longitudinally and thusimparts shrink capabilities to the film. Additional longitudinal ormachine direction racking or stretching may be accomplished by revolvingthe deflate rollers which aid in the collapsing of the "blown bubble" ata greater speed than that of the rollers which serve to transport thereheated "tape" to the racking or blown bubble area. These methods ofracking are well known to those of skill in the art. Preferredtransverse and longitudinal stretching ratios of the present film rangefrom about 3.0 transverse by about 3.0 longitudinal to about 4.0transverse by about 4.0 longitudinal. That is, preferably, the film isstretched between about 3.0 and 4.0 times its original dimensions inboth the transverse and longitudinal directions. More preferably thefilm is stretched between 3.0 and 3.5 times its original dimensions inboth the transverse (TD) and longitudinal (LD) directions. Aparticularly preferred stretching ratio is about 3.3 transverse by about3.3 longitudinal. That is, the particularly preferred film is stretchedabout 3.3 times its original dimensions in both the transverse andlongitudinal directions.

For a film especially useful in conventional packaging applications,preferred transverse and longitudinal stretching ratios of the presentfilm range from about 4.0 transverse by about 4.0 longitudinal to about6.0 transverse by about 6.0 longitudinal. That is, preferably, a film isstretched between about 4.0 and 6.0 times its original dimensions inboth the transverse and longitudinal directions. More preferably thefilm is stretched between 4.5 and 5.5 times its original dimensions inboth the transverse (TD) and longitudinal (MD) directions. Aparticularly preferred stretching ratio is about 5.0 transverse by about5.0 longitudinal. That is, the particularly preferred packaging film isstretched about 5.0 times its original dimensions in both the transverseand longitudinal directions.

To further disclose and clarify the scope of the present invention tothose skilled in the art the following test data are presented.

Two embodiments of the present invention were formed by coextrusion,irradiated and stretched (oriented) by application of internal air(bubble technique) in accordance with the teachings described above.These embodiments were five layered films irradiated with approximately5-6 MR (10 MA-milliamps) and had an approximate layer thickness ratio if1.5/1.5/1/1.5/1.5. Embodiment Y comprised an approximate layer structureof "50%, by weight, A+25%, by weight, B+25%, by weight, C+1,500 ppmD/100%, by weight, A/100%, by weight, C/100%, by weight, A/50%, byweight, A+25%, by weight, B+25%, by weight, C+1,500 ppm D". Embodiment Xcomprised an approximate layer structure of "50%, by weight, A+25%, byweight, B+25%, by weight C+1,500 ppm D/100%, by weight, A/55.6%, byweight, A+27.6%, by weight, B+16.8%, by weight, C/100%, by weight,A/50%, by weight, A+25%, by weight, B+25 %, by weight, C+1,500 ppm D".These two 60 gauge embodiments were compared to a 75 gauge three layerstorm window structure (discussed in Application Ser. No. 609,067 filedMay 10, 1984, hereby incorporated by reference) having an approximatelayer structure of "50%, by weight, A+25%, by weight, B+25%, by weight,C+1,500 ppm D/100%, by weight, A/50%, by weight, A+25%, by weight B+25%,by weight C+1,500 ppm D" and a prior art linear medium densitypolyethylene monolayer structure (discussed above). "A" represents alinear low density polyethylene having a density of about 0.920 gm/cm³(Dowlex 2045). "B" having a linear medium density polyethylene having adensity of about 0.935 gm/cm³ (Dowlex 2037). "C" represents an ethylenevinyl acetate copolymer having from about 3.3% to about 4.1% vinylacetate derived units and a density of from about 0.9232-0.9250 g/cm³(El Paso PE 204CS95). "D" represents a hindered amine stabilizer(TINUVIN® 622).

Test results for these films are listed below in Table I.

                                      TABLE I                                     __________________________________________________________________________                PRESENT   PRESENT   COMPARISON                                                                              PRIOR ART                                       MULTILAYER                                                                              MULTILAYER                                                                              THREE LAYER                                                                             MONOLAYER                                       FILM-Y    FILM-X    FILM      FILM                                __________________________________________________________________________    Approximate Gauge.sup.0                                                                   60        60        75        90                                  Approximate 3.1 MD × 3.4 TD                                                                   3.2 MD × 3.4 TD                                                                   3.0 MD × 3.0 TD                                                                   4.8 MD × 4.5 TD               Racking Ratio                                                                 Tensile At Break                                                              And 73° F. (PSI).sup.1                                                 Av..sup.2 Long.                                                                           133.1 × 100                                                                       175.6 × 100                                                                       135.7 × 100                                                                       204.5 × 100                   Std. Dev.   5.6 × 100                                                                         12.1 × 100                                                                        16.6 × 100                                                                        3.7 × 100                     95% C.L..sup.3                                                                            8.9 × 100                                                                         19.2 × 100                                                                        26.5 × 100                                                                        5.9 × 100                     Av. Trans.  197.0 × 100                                                                       172.3 × 100                                                                       128.3 × 100                                                                       207.5 × 100                   Std. Dev.   24.0 × 100                                                                        8.5 × 100                                                                         17.4 × 100                                                                        11.7 × 100                    95% C.L.    38.1 × 100                                                                        13.6 × 100                                                                        27.6 × 100                                                                        18.5 × 100                    Elongation At Break                                                           And 73° F. (%).sup.4                                                   Av. Long.   168       222       221       170                                 Std. Dev.   7         11        20        2                                   95% C.L.    11        18        32        3                                   Av. Trans.  128       205       226       112                                 Std. Dev.   25        12        12        11                                  95% C.L.    39        19        20        17                                  Modulus At 73° F.                                                      (PSI).sup.5                                                                   Av. Long.   27.4 × 1000                                                                       30.8 × 1000                                                                       22.3 × 1000                                                                       --                                  Std. Dev.    0.7 × 1000                                                                        1.7 × 1000                                                                        2.2 × 1000                                                                       --                                  95% C.L.     1.1 × 1000                                                                        2.8 × 1000                                                                        3.5 × 1000                                                                       --                                  Av. Trans.  32.5 × 1000                                                                       33.8 × 1000                                                                       26.1 × 1000                                                                       --                                  Std. Dev.    1.4 × 1000                                                                        3.4 × 1000                                                                        0.9 × 1000                                                                       --                                  95% C.L.     2.2 × 1000                                                                        5.4 × 1000                                                                        1.4 × 1000                                                                       --                                  Tear Propagation                                                              At 73° F. (grams).sup.6                                                Av. Long.   7.20      6.85      29.13     13.38                               Std. Dev.   0.85      0.34      6.25      0.32                                95% C.L.    1.35      0.54      9.94      0.51                                Av. Trans.  4.80      6.75      30.38     13.31                               Std. Dev.   1.10      0.68      15.28     2.25                                95% C.L.    1.74      1.08      24.31     3.56                                Ball Burst Impact                                                             At 73° F. 1.00 In.                                                     Diam. Sphere Hd.                                                              (cm × kg).sup.7                                                         Average     12.9      14.2      37.3      23.6                                Std. Dev.   0.8       1.3       3.4       2.7                                 95% C.L.    1.3       2.0       5.4       4.3                                 Optical Properties                                                            At 73° F.                                                              Haze (%).sup.8                                                                Avg.        2.4       2.8       3.9       1.6                                 Std. Dev.   0.2       0.3       0.7       0.2                                 95% C.L.    0.3       0.5       1.1       0.3                                 Gloss (45°).sup.9                                                      Avg.        89        87        82        93.3.sup.9a                         Std. Dev.   2         2         4         1.0                                 95% C.L.    3         3         6         1.5                                 Tensile At 20                                                                 In./Min. And                                                                  73° F. (PSI).sup.10                                                    5% Elongation                                                                 Av. Long.   16.0 × 100                                                                        17.5 × 100                                                                        13.5 × 100                                                                        --                                  Std. Dev.   1.4 × 100                                                                         1.7 × 100                                                                         1.3 × 100                                                                         --                                  95% C.L.    2.2 × 100                                                                          2.7 × 1000                                                                       2.0 × 100                                                                         --                                  Av. Trans.  19.2 × 100                                                                        18.4 × 100                                                                        13.7 ×  100                                                                       --                                  Std. Dev.   1.7 × 100                                                                         1.2 × 100                                                                         1.5 × 100                                                                         --                                  95% C.L.    2.7 × 100                                                                         1.9 × 100                                                                         2.4 × 100                                                                         --                                  10% Elongation                                                                Av. Long.   24.1 × 100                                                                        25.5 × 100                                                                        22.1 × 100                                                                        --                                  Std. Dev.   1.2 × 100                                                                         1.4 × 100                                                                         1.4 × 100                                                                         --                                  95% C.L.    2.0 × 100                                                                         2.2 × 100                                                                         2.2 × 100                                                                         --                                  Av. Trans.  27.8 × 100                                                                        27.1 × 100                                                                        20.1 × 100                                                                        --                                  Std. Dev.   2.5 × 100                                                                         1.2 × 100                                                                         1.0 × 100                                                                         --                                  95% C.L.    3.9 × 100                                                                         1.9 × 100                                                                         2.8 × 100                                                                         --                                  15% Elongation                                                                Av. Long.   29.1 × 100                                                                        31.4 × 100                                                                        29.0 × 100                                                                        --                                  Std. Dev.   1.7 × 100                                                                         0.8 × 100                                                                         1.9 × 100                                                                         --                                  95% C.L.    2.7 × 100                                                                         1.3 × 100                                                                         3.1 × 100                                                                         --                                  Av. Trans.  35.0 ×  100                                                                       35.5 × 100                                                                        24.0 × 100                                                                        --                                  Std. Dev.   3.1 × 100                                                                         2.7 × 100                                                                         2.2 × 100                                                                         --                                  95% C.L.    5.0 × 100                                                                         4.3 × 100                                                                         3.5 × 100                                                                         --                                  20% Elongation                                                                Av. Long.   32.8 × 100                                                                        35.4 × 100                                                                        34.4 × 100                                                                        --                                  Std. Dev.   1.7 × 100                                                                         1.1 × 100                                                                         1.9 × 100                                                                         --                                  95% C.L.    2.7 × 100                                                                         1.7 × 100                                                                         3.0 × 100                                                                         --                                  Av. Trans.  40.9 × 100                                                                        41.6 × 100                                                                        26.7 × 100                                                                        --                                  Std. Dev.   4.4 × 100                                                                         5.8 × 100                                                                         2.2 × 100                                                                         --                                  95% C.L.    7.0 × 100                                                                         5.8 × 100                                                                         3.5 × 100                                                                         --                                  25% Elongation                                                                Av. Long.   35.8 × 100                                                                        38.1 × 100                                                                        38.0 × 100                                                                        --                                  Std. Dev.   1.8 × 100                                                                         0.7 × 100                                                                         2.2 × 100                                                                         --                                  95% C.L.    2.9 × 100                                                                         1.1 × 100                                                                         3.5 × 100                                                                         --                                  Av. Trans.  46.3 × 100                                                                        48.1 × 100                                                                        29.6 × 100                                                                        --                                  Std. Dev.   5.3 × 100                                                                         4.4 × 100                                                                         2.7 × 100                                                                         --                                  95% C.L.    8.5 × 100                                                                         7.0 × 100                                                                         4.3 × 100                                                                         --                                  Shrink Properties                                                             At 200° F.                                                             Free Shrink (%).sup.11                                                        Av. Long.   17        18        29        2                                   Std. Dev.   2         2         2         1                                   95% C.L.    3         3         3         2                                   Av. Trans.  27        26        30        11                                  Std. Dev.   2         1         2         1                                   95% C.L.    3         1         3         1                                   Shrink Force (lbs.).sup.12                                                    Av. Long.   0.223     0.226     0.439     0.028                               Std. Dev.   0.017     0.009     0.084     0.010                               95% C.L.    0.027     0.015     0.133     0.015                               Av. Trans.  0.433     0.368     0.425     0.496                               Std. Dev.   0.018     0.009     0.018     0.023                               95% C.L.    0.029     0.014     0.028     0.036                               Shrink Tension (PSI).sup.13                                                   Av. Long.   274       307       381       29                                  Std. Dev.   26        14        30        11                                  95% C.L.    42        22        48        17                                  Av. Trans.  431       508       404       494                                 Std. Dev.   8         7         43        33                                  95% C.L.    12        10        68        52                                  __________________________________________________________________________

An alternate embodiment was formed by coextrusion, stretched (oriented)by application of internal air (bubble technique) in accordance with theteachings described above. This embodiment was a five layer film and hadan approximate layer thickness ratio of 2/1.5/1/1.5/2. The approximatelayer structure of this embodiment comprised 50%, by weight, A plus 25%,by weight, B plus 25%, by weight, C/100%, by weight, A/100%, by weight,C/100%, by weight, A/50%, by weight, A plus 25%, by weight, B plus 25%,by weight, C. This embodiment Z has a thickness of 60 gauge. Testresults for this film, particularly suited for packaging applications,is listed below in Table II. The multilayer film was irradiated, with anestimated irradiation of about 2.5 MR based on the flow rate data asshown in Table II below. The physical properties of the alternateembodiment, shown in Table II, are compared with a three layer film likethat of the three layer of Table I but without the presence of UVstabilizer, and with a racking ratio of 5.2 MD by 4.8 TD.

                  TABLE II                                                        ______________________________________                                                   PRESENT     COMPARISON                                                        MULTILAYER  THREE LAYER                                                       FILM-Z      FILM                                                   ______________________________________                                        Approximate Gauge.sup.0                                                                    60            60                                                 Approximate  5.2 MD × 4.8 TD                                                                       5.2 MD × 4.8 TD                              Racking Ratio                                                                 Tensile At Break                                                              And 73° F. (PSI).sup.1                                                 Av..sup.2 Long.                                                                            147.5 × 100                                                                           165.2 × 100                                  Std. Dev.    9.6 × 100                                                                             10.7 × 100                                   95% C.L..sup.3                                                                             15.2 × 100                                                                            17.0 × 100                                   Av. Trans.   157.3 × 100                                                                           197.5 × 100                                  Std. Dev.    14.0 × 100                                                                            11.2 × 100                                   95% C.L.     22.2 × 100                                                                            17.8 × 100                                   Elongation At Break                                                           And 73° F. (%).sup.4                                                   Av. Long.    122           113                                                Std. Dev.    6             6                                                  95% C.L.     10            10                                                 Av. Trans.   108           111                                                Std. Dev.    13            6                                                  95% C.L.     20            9                                                  Modulus At 73° F.                                                      (PSI).sup.5                                                                   Av. Long.    52.7 × 1000                                                                           49.9 × 1000                                  Std. Dev.     1.7 × 10000                                                                           4.0 × 1000                                  95% C.L.      2.6 ×  1000                                                                           6.4 × 1000                                  Av. Trans.   56.1 × 1000                                                                           49.5 × 1000                                  Std. Dev.     1.4 × 1000                                                                            0.8 × 1000                                  95% C.L.      2.2 × 1000                                                                            1.3 × 1000                                  Tear Propagation                                                              At 73° F. (grams).sup.6                                                Av. Long.    5.35          5.10                                               Std. Dev.    0.50          0.38                                               95% C.L.     0.80          0.61                                               Av. Trans.   5.35          7.65                                               Std. Dev.    1.12          1.03                                               95% C.L.     1.79          1.65                                               Ball Burst Impact                                                             At 73° F. 1.00 In.                                                     Diam. Sphere Hd.                                                              (cm × kg).sup.7                                                         Average      19.3          18.5                                               Std. Dev.    2.3           1.5                                                95% C.L.     3.6           2.3                                                Optical Properties                                                            At 73° F.                                                              Haze (%).sup.8                                                                Avg.         2.2           1.9                                                Std. Dev.    0.3           0.3                                                95% C.L.     0.5           0.6                                                Gloss (45°).sup.9                                                      Avg.         92            91                                                 Std. Dev.    2             2                                                  95% C.L.     2             3                                                  Shrink Properties                                                             At 200° F.                                                             Free Shrink (%).sup.11                                                        Av. Long.    13            13                                                 Std. Dev.    1             2                                                  95% C.L.     2             3                                                  Av. Trans.   19            18                                                 Std. Dev.    1             1                                                  95% C.L.     1             1                                                  Shrink Force (lbs.).sup.12                                                    Av. Long.    0.203         0.221                                              Std. Dev.    0.018         0.024                                              95% C.L.     0.028         0.038                                              Av. Trans.   0.316         0.324                                              Std. Dev.    0.009         0.011                                              95% C.L.     0.014         0.018                                              Shrink Tension                                                                (PSI).sup.13                                                                  Av. Long.    278           291                                                Std. Dev.    15            11                                                 95% C.L.     24            17                                                 Av. Trans.   455           455                                                Std. Dev.    15            9                                                  95% C.L.     23            15                                                 Shrink Properties                                                             At 220° F.                                                             Free Shrink (%).sup.11                                                        Av. Long.    23            21                                                 Std. Dev.    1             2                                                  95% C.L.     1             4                                                  Av. Trans.   34            29                                                 Std. Dev.    1             2                                                  95% C.L.     1             3                                                  Shrink Force (lbs.).sup.12                                                    Av. Long.    0.249         0.253                                              Std. Dev.    0.023         0.020                                              95% C.L.     0.036         0.032                                              Av. Trans.   0.359         0.369                                              Std. Dev.    0.003         0.005                                              95% C.L.     0.004         0.008                                              Shrink Tension                                                                (PSI).sup.13                                                                  Av. Long.    339           350                                                Std. Dev.    17            11                                                 95% C.L.     26            18                                                 Av. Trans.   537           504                                                Std. Dev.    7             6                                                  95% C.L.     11            9                                                  Shrink Porperties                                                             At 240° F.                                                             Free Shrink (%).sup.11                                                        Av. Long.    50            54                                                 Std. Dev.    4             2                                                  95% C.L.     6             3                                                  Av. Trans.   58            57                                                 Std. Dev.    1             1                                                  95% C.L.     1             1                                                  Shrink Force (lbs.).sup.12                                                    Av. Long.    0.265         0.245                                              Std. Dev.    0.010         0.008                                              95% C.L.     0.016         0.013                                              Av. Trans.   0.354         0.360                                              Std. Dev.    0.013         0.008                                              95% C.L.     0.020         0.013                                              Shrink Tension                                                                (PSI).sup.13                                                                  Av. Long.    370           392                                                Std. Dev.    8             6                                                  95% C.L.     13            10                                                 Av. Trans.   500           567                                                Std. Dev.    19            15                                                 95% C.L.     30            23                                                 Shrink Properties                                                             At 260° F.                                                             Free Shrink (%).sup.11                                                        Av. Long.    78            78                                                 Std. Dev.    1             1                                                  95% C.L.     1             1                                                  Av. Trans.   79            77                                                 Std. Dev.    1             1                                                  95% C.L.     2             2                                                  Shrink Force (Lbs.).sup.12                                                    Av. Long.    0.245         0.264                                              Std. Dev.    0.032         0.035                                              95% C.L.     0.051         0.056                                              Av. Trans.   0.355         0.310                                              Std. Dev.    0.017         0.014                                              95% C.L.     0.027         0.022                                              Shrink Tension                                                                (PSI).sup.13                                                                  Av. Long.    360           391                                                Std. Dev.    15            15                                                 95% C.L.     24            25                                                 Av. Trans.   505           483                                                Std. Dev.    28            21                                                 95% C.L.     44            33                                                 Coefficient of Friction                                                       At 73° F..sup.14                                                       Av. In/In                                                                     Static       0.313         0.670                                              Std. Dev.    0.010         0.376                                              95% C.L.     0.016         0.598                                              Av. In/In                                                                     Kinetic      0.284         0.325                                              Std. Dev.    0.007         0.119                                              95% C.L.     0.011         0.189                                              Av. Out/Out                                                                   Static       0.292         1.010                                              Std. Dev.    0.002         0.524                                              95% C.L.     0.003         0.833                                              Av. Out/Out                                                                   Kinetic      0.263         0.444                                              Std. Dev.    0.009         0.234                                              95% C.L.     0.015         0.372                                              Flow Rate At 230° C.                                                   and 21600 grams                                                               load (grams/ten                                                               minutes).sup.15                                                               Sample 1     3.42          3.13                                               Sample 2     3.33          3.63                                               Sample 3     3.14          3.58                                               Oxygen Transmission                                                           At 73° F.                                                              [cc STP/(24 hrs.,                                                             square M, ATM)].sup.16                                                        Sample 1     9361.2        8125.0                                             Sample 2     10372.4       11046.9                                            Sample 3     9884.6        10174.9                                            Water Vapor                                                                   Transmission                                                                  At 100° F.                                                             [grams/(24 hours,                                                             100 square inches)]                                                           at 100% RH.sup.17                                                             Sample 1     1.69                                                             Sample 2     1.87                                                             Sample 3     1.62                                                             ______________________________________                                         The following footnotes apply to Tables I and II.                             .sup.0 100 gauge is equal to 1 mil. The measured thickness of a given fil     will vary significantly (on the order of 40%) from point to point.            .sup.1 ASTM D88281                                                            .sup.2 All values in Table I are averages obtained from four (4) replicat     measurements.                                                                 .sup.3 C.L. Is Confidence Limit  for example, if the reported average         value was 10 and the 95% C.L. was 2, then if 100 replicate readings were      made, 95 of them would have a value between 8 and 12, inclusive.              .sup.4 ASTM D88281                                                            .sup.5 ASTM D88281                                                            .sup.6 ASTM D193879                                                           .sup.7 ASTM D342080                                                           .sup.8 ASTM D100361 (reapproved 1977)                                         .sup.9 ASTM D245770 (reapproved 1977)                                         .sup. 9a Outside surface measurement.                                         .sup.10 ASTM D88281                                                           .sup.11 ASTM D273270 (reapproved 1976)                                        .sup.12 ASTM D283881 (shrink force = shrink tension × film thicknes     in mils × 1000)                                                         .sup.13 ASTM D283881                                                          .sup.14 ASTM Sled; ASTM D189478                                               .sup.15 ASTM D 132879                                                         .sup.16 ASTM D 3985                                                           .sup.17 ASTM F 372                                                       

It should be noted that the prior art mono-layer storm window film didnot contain any ultraviolet light stabilizers since this film wasintended for use on the interior surface of the window and, accordingly,would not be substantially subjected to ultraviolet light waves.

The data above demonstrates that the present exterior storm window filmgenerally has improved values for (1) haze and (2) gloss as compared tothe three layer film. Accordingly, the present storm window film is moredesirably adapted for use as an exterior storm window. This differencemay be attributable to the different additive package employed in thefilms.

The tear propagation and ball burst values of the two embodiments of thepresent film are less than those values for the three layer exteriorstorm window comparison film and the prior art monolayer interior stormwindow film. This is believed to result from the fact that embodiments Xand Y are approximately (see footnote 1) 60 gauge in thickness and thethree layer and monolayer films are 75 gauge and 90 gauge in thickness,respectively. The present embodiments exhibit good tear propagation andball burst values for film of approximately 60 gauge.

It should be understood that the detailed description and specificexamples which indicate the presently preferred embodiments of theinvention are given by way of illustration only since various changesand modifications within the spirit and scope of the appended claimswill become apparent to those of ordinary skill in the art upon reviewof the above detailed description and examples.

In view of the above I claim:
 1. An oriented multilayer filmcomprising:a cross-linked core layer comprising either (a) an ethylenevinyl acetate copolymer or (b) a three component blend of (1) a linearlow density polyethylene, (2) a linear medium density polyethylene and(3) an ethylene vinyl acetate copolymer; two cross-linked interiorlayers each comprising a linear low density polyethylene; and twocross-linked surface layers each comprising a three component blend of(1) a linear low density polyethylene, (2) a linear medium densitypolyethylene, and (3) an ethylene vinyl acetate copolymer, said blendbeing free of ultraviolet light stabilizers.
 2. An oriented five layerfilm adapted for use as a packaging material comprising:a cross-linkedcore layer comprising either (a) an ethylene vinyl acetate copolymer or(b) a three component blend of (1) from about 40%, by weight, to about60%, by weight, of a linear low density polyethylene, (2) from about20%, by weight, to about 30%, by weight, of a linear medium densitypolyethylene and (3) from about 20%, by weight, to about 30%, by weight,of an ethylene vinyl acetate copolymer; two cross-linked intermediatelayers each comprising a linear low density polyethylene; and twocross-linked surface layers each comprising a three component blend of(1) from about 40% to about 60%, by weight, of a linear low densitypolyethylene, (2) from about 20% to about 30%, by weight, of a linearmedium density polyethylene, and (3) from about 20% to about 30%, byweight, of an ethylene vinyl acetate copolymer, said blend being free ofultraviolet light stabilizers.
 3. An oriented five layer film adaptedfor use as a packaging material comprising:a cross-linked core layerconsisting essentially of either (a) about 100%, by weight, of anethylene vinyl acetate copolymer comprising from about 3.3% to about4.1% vinyl acetate derived units, said ethylene vinyl acetate copolymerhaving a density of from about 0.9232 to about 0.9250 grams per cubiccentimeter at 23 degrees Centigrade or (b) a three component blend of(1) about 55%, by weight, of a linear low density polyethylene having adensity of about 0.920 grams per cubic centimeter at 23 degreescentigrade, (2) about 28%, by weight of a linear medium densitypolyethylene having a density of about 0.935 grams per cubic centimeterat 23 degrees centigrade and (3) about 17%, by weight, of an ethylenevinyl acetate copolymer comprising from about 3.3% to about 4.1% vinylacetate derived units, said ethylene vinyl acetate copolymer having adensity of from about 0.9232 to about 0.9250 grams per cubic centimeterat 23 degrees centigrade; two cross-linked intermediate layers eachconsisting essentially of about 100%, by weight, of a linear low densitypolyethylene having a density of about 0.920 grams per cubic centimeterat 23 degrees centigrade; and two cross-linked surface layers eachconsisting essentially of a three component blend of (1) about 50%, byweight, of a linear low density polyethylene having a density of about0.920 grams per cubic centimeter at 23 degrees centigrade, (2) about25%, by weight, of a linear medium density polyethylene having a densityof about 0.935 grams per cubic centimeter at 23 degrees centigrade, and(3) about 25%, by weight, of an ethylene vinyl acetate copolymercomprising from about 3.3% to about 4.1% vinyl acetate derived units,said ethylene vinyl acetate copolymer having a density of from about0.9232 to about 0.9250 grams per cubic centimeter at 23 degreescentigrade, said blend being free of ultraviolet light stabilizers. 4.The film of claim 2 wherein said ethylene vinyl acetate copolymercomprises from about 2%, by weight, to about 18%, by weight, of vinylacetate derived units.
 5. The film of claim 2 wherein said vinyl acetatecopolymer comprises from about 2%, by weight, to about 10%, by weight,of vinyl acetate derived units.
 6. The film of claim 2 wherein saidethylene vinyl acetate copolymer comprises from about 2%, by weight, toabout 5%, by weight, of vinyl acetate derived units.
 7. The film ofclaims 2 or 3 further comprising a colorant additive to at least one ofsaid layers.
 8. The film of claims 2 or 3 further comprising a colorantadditive solely in said core layer.
 9. The film of claims 2 or 3 whichhas been cross-linked with from about 1 MR to about 5 MR of irradiation.10. The film of claims 2 or 3 which has been cross-linked with fromabout 2 MR to about 4 MR of irradiation.
 11. The film of claims 2 or 3which has been cross-linked with about 3 MR of irradiation.
 12. The filmof claims 2 or 3 which has been oriented by racking at a racking ratioof from about 4.0 to about 6.0 in both the longitudinal and transversedirections.
 13. The film of claims 2 or 3 which has been oriented byracking at a racking ratio of from about 4.5 to about 5.5 in both thelongitudinal and transverse directions.
 14. The film of claims 2 or 3wherein (a) the thicknesses of the two surface layers are substantiallyequal to each other and the sum of the thicknesses of the two surfacelayers comprise from about 40% to about 60% of the total thickness ofthe film, (b) the thicknesses of the two intermediate layers aresubstantially equal to each other and the sum of the thicknesses of thetwo intermediate layers comprises from about 40% to about 60% of thetotal thickness of the film, (c) the thickness of the core layercomprises from about 10% to about 30% of the total film thickness and(d) the total film thickness is from about 50 gauge to about 200 gauge.15. The film of claim 14 wherein the thickness of the core layercomprises about 14% of the total film thickness and the thickness of thetwo intermediate and the two surface layers each comprise about 21.5% ofthe total film thickness.
 16. An oriented five layer film adapted foruse as a packaging material comprising:a cross-linked core layercomprising either (a) an ethylene vinyl acetate copolymer or (b) a threecomponent blend of (1) from about 40%, by weight, to about 60%, byweight, of a linear low density polyethylene, (2) from about 20%, byweight, to about 30%, by weight, of a linear medium density polyethyleneand (3) from about 20%, by weight, to about 30% by weight, of anethylene vinyl acetate copolymer; two cross-linked intermediate layerseach comprising a linear low density polyethylene; and two cross-linkedsurface layers each comprising a three component blend of (1) from about40% to about 60%, by weight, of a linear low density polyethylene, (2)from about 20% to about 30%, by weight, of a linear medium densitypolyethylene, and (3) from about 20% to about 30%, by weight, of anethylene vinyl acetate copolymer; the film oriented by racking at aracking ratio of about 5.0 in both the longitudinal and transversedirections.
 17. An oriented multilayer film comprising:a cross-linkedcore layer comprising either (a) an ethylene vinyl acetate copolymer or(b) a three component blend of (1) a linear low density polyethylene,(2) a linear medium density polyethylene and (3) an ethylene vinylacetate copolymer; two cross-linked interior layers each comprising alinear low density polyethylene; and two cross-linked surface layerseach comprising a three component blend of (1) a linear low densitypolyethylene, (2) a linear medium density polyethylene, and (3) anethylene vinyl acetate copolymer; the film biaxially oriented in therange of about 4.0 to about 6.0 times the original dimensions in boththe transverse and longitudinal directions.